Anaerobic Respiration

Page 1: Title Page

• Second Edition

• Book Title: Prescott's Principles of Microbiology

• Authors: Joanne Willey, Kathleen Sandman

• Topic: Anaerobic Respiration

Page 2: Overview of Anaerobic Respiration

• Definition: Anaerobic respiration can occur when oxygen is not available, utilizing alternative terminal electron acceptors.

• Common Acceptors Include:

  • Metals

  • Oxidized ions of nitrogen

  • Sulfur

• Typical Environments:

  • Wetland soil

  • Human digestive tract

Page 3: Characteristics of Anaerobic Respiration

• Uniqueness to Prokaryotes: Anaerobic respiration is exclusive to prokaryotic organisms.

• Alternative Electron Acceptors:

  • Some bacteria utilize nitrate (NO3) reducing it to nitrite (NO2)

  • Others use sulfur compounds, reducing sulfate (SO42–) to sulfite (SO32–)

Page 4: Table of Electron Acceptors in Respiration

Page 5: Nitrate Reduction Process

• Key Steps:

  1. Nitrate (NO3) is reduced via Nitrate Reductase to nitrite (NO2)

  2. Detection with sulfanilic acid (Nitrate Reagent A)

  3. Further reduction leads to nitric oxide (NO) via nitrite reductase, then to nitrous oxide (N2O), and finally nitrogen gas (N2)

• Testing Methodology:

  • Use of reagents to indicate presence of nitrite and final products (e.g., color change with Prontosil)

Page 6: Mechanism of Sulfate-Reducing Bacteria

• Process: Oxidation of hydrogen (H₂) to create a proton motive force.

  • H₂ is oxidized releasing protons (8H+) and electrons (8e)

• Reduced Products: H₂S (hydrogen sulfide)

• Electron Transport Chain Components:

  • Involves various enzyme complexes and electron carriers (e.g., cyt C3 and FADH) producing ATP from ADP

Page 7: Properties of Anaerobic Respiration

• General Characteristics:

  • Utilizes electron carriers other than O2

  • Typically yields less ATP due to less positive reduction potentials compared to O2

• Shorter Electron Transport Chain:

  • Less hydrogen pumped out

• Dissimilatory Nitrate Reduction:

  • Nitrate is used as a terminal electron acceptor; not available for cellular assimilation

• Denitrification:

  • Converts nitrate to nitrogen gas causing loss of soil fertility

Page 8: Electron Transport Chain (ETC) in Anaerobic Respiration

• Example Organism: Paracoccus denitrificans

• Differences Compared to Aerobic ETC:

  • More complex and branched

  • Different electron carriers used

• Denitrification Steps:

  1. Nitrate → Nitrite

  2. Nitrite → Nitric Oxide

  3. Nitric Oxide → Nitrous Oxide

  4. Nitrous Oxide → N2

Page 9: Important Terms

• Dissimilatory Nitrate Reduction:

  • Conversion of nitrogen allowing cellular use for amino acids and nucleotides.

• Denitrification:

  • Release of nitrogen gas (N2) into the atmosphere, contributing to nitrogen cycles and soil health.